Image Processing Reference
In-Depth Information
shared resources in the system) and the name of the data they produce. he scheduler needs all this
information to take the decisions.
From the point of view of the operating system, a new component that takes care of all the data
exchange needs to be implemented. his would in fact be an extended message-passing mechanism,
withtheaddedfeatureofnotifyingtheschedulerwhennewdatatypesbecomeavailable.hemapping
of this module in the architecture is the constraint imposed to the protocols to send/receive data via,
for example, a publish/subscribe mechanism to the central scheduler.
An efficient naming system for the entities and the data is needed. Downloading new entities to a
sensor node involves issues similar to services discovery. Several entities with the same functionality
but with diferent requirements and capabilities might coexist. he data-centric scheduler has to make
thedecisionwhichoneisthebest.
The architecture presented earlier might be extended to groups of sensor nodes. Several data-
centric schedulers together with a small, fixed number of protocols can communicate with each other
and form a virtual backbone of the network [].
Entities running inside sensor nodes can be activated using data types that become available at
other sensor nodes (for example, imagine one node using his neighbor routing entity because it needs
the memory to process some other data).
Of course, this approach raises new challenges. A naming system for the functionality and data
types,reliabilityissuesofthesystem(forfactorssuchasmobility,communicationfailures,nodefail-
ures, and security attacks), etc. are just a few examples. Related work on these topics already exist
(e.g., [,]). In the case of the data-centric architecture we propose, this aspect is a research topic
addressed by the Featherlight research project [].
4.3.4 Generalized Component Interfaces
Sensornetworksarearelativelynewieldofscience.Alargenumberofprototypeshavebeenalready
built and some commercial application already exist. One of the main problems a system integrator
faces at this moment is the lack of standards and basically the lack of a standardized interface to the
data available via the sensor networks.
The lack of standardized interfaces manifests itself at various levels: the interface between appli-
cation and the architecture, interface between application and networking protocols, interface
between the gateway and an external computer, and the interface between the computer and existing
infrastructure. The end result of this lack of standardization reflects itself in the usability of sensor
networksandtheiradoptionbythegeneralpublic.Applicationsarewrittennowmainlyforspeciic
platforms and specific networking protocol stacks and sharing of data between various applications
needs to be implemented almost from scratch every time.
In this section we will explore one alternative for such an interface. he motivation for this effort
is quite straight forward—we can only bring into discussion the fact that interfacing the various
building blocks of a sensor network takes more development time then implementing the spe-
cific application. The existence of a generally accepted interface will allow various protocols to be
actually stacked on top of each other; it will also allow quantification of the behavior of various algo-
rithms/protocols in a given setup. Other benefits of having such an interface would be reducing the
number of interfaces needed to access all the data provided by the sensors in the network, reducing
the number of packet formats to be transmitted by the MAC and routing protocols, etc.
The starting point for the generalized component interface is the concept of entity itself. As
mentioned previously, by entity we understand a basic software component having a dedicated func-
tionality. he entity provides already a number of parameters as the details needed for the real time
scheduler, the details about the data it produces and it consumes, etc. We extend this information
with a description on the way the actual entities provide functionality to the exterior.
